This application claims Paris Convention priority of Japanese Application No. 2003-023148 filed Jan. 31, 2003, the entire disclosure of which is hereby incorporated by reference.
The present invention relates to a method of manufacturing a silicon single crystal ingot by pulling it from a silicon melt at a pull rate such that the interior of the silicon single crystal ingot becomes a perfect region. The invention also relates to ingots manufactured by this method.
Conventionally, a method of pulling a silicon single crystal ingot according to a Czochralski method (hereinafter also referred to as a CZ method) has been known as a method of manufacturing silicon single crystal ingots. In the CZ method, a silicon melt stored in a quartz crucible is brought into contact with a seed crystal and the seed crystal is pulled up while rotating the quartz crucible and the seed crystal, whereby a columnar silicon single crystal ingot is manufactured.
Meanwhile, it has been pointed out that yield reduction in a process of manufacturing semiconductor integrated circuits arises from the presence of microdefects of oxygen precipitates that become nuclei of oxidation induced stacking fault (hereinafter referred to as “OSF”), crystal originated particle, (hereinafter referred to as “COP”), interstitial-type large dislocation (hereinafter referred to as “L/D”) and the like. The microdefects that become the nuclei of OSF are introduced during crystal growth, and OSF is exposed during a thermal oxidation process or the like in the manufacture of semiconductor devices, causing faults in the manufactured devices, such as an increase in leakage current. COP is a pit arising from a crystal that is detected on a wafer surface when the silicon wafer that has undergone a mirror polishing is washed with a mixed solution of ammonia and hydrogen peroxide. The pit is also detected as a light scattering defect along with real particles when the wafer is measured with a particle counter.
COP becomes a cause of deteriorating electrical characteristics, such as a time dependent dielectric breakdown (TDDB) characteristic and a time zero dielectric breakdown (TZDB) characteristic of oxide films. In addition, COP existing on a wafer surface can create a height difference in a wiring process of devices, which can become a cause of wire breakage. Moreover, it becomes a cause of leakage in element-isolating portions, lowering product yield. L/D is also called dislocation cluster, or dislocation pit, because the silicon wafer containing this defect produces a pit when immersed in a selective etchant solution containing hydrofluoric acid as a main component. This L/D also becomes a cause of deteriorating electrical characteristics, such as leakage characteristics, isolation characteristics, and the like. For these reasons, it has been necessary to reduce OSF, COP, and L/D defects in silicon wafers used in the manufacture of semiconductor integrated circuits.
A method of manufacturing a single crystal silicon ingot for cutting out defect-free silicon wafers having no OSF, COP, and L/D defects has been disclosed (see, for example, U.S. Pat. No. 6,045,610 and the corresponding Japanese Unexamined Patent Publication No. 11-1393). Generally, pulling a silicon single crystal ingot at a fast rate produces a region [V] inside the ingot in which agglomerates of vacancy-type point defects are present dominantly, whereas pulling the ingot at a slow rate forms a region [I] inside the ingot in which agglomerates of interstitial silicon-type point defects are present dominantly. In view of this, by pulling an ingot at an optimum pull rate, the above-mentioned manufacturing method makes it possible to manufacture a silicon single crystal ingot made of a perfect region [P] in which the agglomerates of the point defects do not exist.
In the above-described conventional method of manufacturing a silicon single crystal ingot, however, it is necessary to control the axial temperature gradient in the vicinity of the solid-liquid interface between the silicon single crystal ingot and the silicon melt so that it becomes uniform. This control is affected by a change in the remaining quantity of the silicon melt and a change in its convection. For this reason, it has been difficult to manufacture a silicon single crystal ingot that is defect-free over the entire length of the straight cylindrical body of the ingot.